I don't know what the presale checker sources from but it does look like you have a case. You could perhaps try to raise their attention on Reddit. I think Hudson Jameson (u/souptacular) is the community rep now, maybe try and DM him there.

Hi @BeeFer310, did you ever get your presale wallet to import successfully. I've never been able to, I have receipt of sell and presale wallet, but it doesn't import, should be 1600. Apparently this is an issue for several others, including myself. I'm trying to get a support group together for those who still can't access their presale wallet. Maybe together we can figure out a way to solve this since Ethereum, [email protected], is unresponsive and they closed their helpdesk email address.